The present invention relates to a polygonal mirror type scanner included in an electrophotographic copier, laser printer, facsimile apparatus or similar image forming apparatus. More particularly, the present invention relates to a rotary body included in a polygonal mirror type scanner and a method of machining the same.
A polygonal mirror type scanner for the above application includes a scanner motor made up of a rotor portion and a stator portion. The rotor portion includes a flange on which a polygonal mirror is mounted. The scanner motor causes the polygonal mirror to rotate while reflecting light incident thereto and representative of image data. A magnet is mounted on the bottom or the inner circumference of a rotor yoke also included in the rotor portion.
To produce the above scanner motor, a rotary shaft is inserted in the flange while a rotor is affixed to the flange, in parallel with the machining of a flat polygonal mirror. The machined polygonal mirror is mounted to the subassembly of the flange, rotary shaft and rotor. Thereafter, the axis of rotation of the polygonal mirror is aligned with the axis of the rotary shaft and then fixed in place.
However, the problem with the above conventional scanner is that it is bulky because the polygonal mirror and scanner motor are physically separate from each other and because the scanner motor cannot be sufficiently reduced in size. The scanner therefore occupies a substantial space when mounted to a laser printer or similar image forming apparatus, obstructing the miniaturization of the apparatus.
In light of the above, Japanese Patent Laid-Open Publication No. 8-62527, for example, discloses a scanner motor constructed to miniaturize a polygonal mirror type scanner. The scanner motor taught in this document includes a hexagonal rotor yoke and chip mirrors separate from the rotor yoke. The chip mirrors are adhered to the hexagonal circumferential surfaces of the rotor yoke.
The chip mirrors, however, not only increase the number of parts of the scanner, but also need highly accurate adhesion to the rotor yoke. In addition, the chip mirrors are apt to come off or deform after adhesion due to a centrifugal force. Further, because a permanent magnet is mounted on the flat bottom of the rotor yoke, should the permanent magnet be inaccurately positioned relative to the rotor yoke, the magnet and shaft would become offset. This would disturb the dynamic balance and would thereby degrade the jitter characteristic and bring about oscillation and noise. Moreover, the rotor yoke is apt to come off or deform due to a centrifugal force. In addition, the positional adjustment of the polygonal mirror relative to the shaft needs highly accurate measuring means and affixing means.
Japanese Patent Laid-Open Publication No. 5-241090 proposes a polygonal mirror including a ceramic ring, a yoke and a rotor magnet constructed integrally with each other by casting aluminum. After the surfaces of the ceramic ring, yoke and rotor magnet have been machined, mirror surfaces are formed by deposition. However, a magnet positioned below the mirror surfaces is apt to reduce the accuracy of the mirror surfaces due to a centrifugal force acting on the magnet during high-speed rotation.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 5-257078, 7-287183, 62-164017, 9-230269, and 6-98517.